Discussion
What is the correct order of decreasing crystallinity of the given polymers?
P atactic-Polypropylene
Q syndiotactic-Polystyrene
R Nylon 6
S Polyethylene terephthalate
Answer: D
The key gives option D: PET > Nylon 6 > syndiotactic polystyrene > atactic polypropylene. I could confirm only the last place with certainty; I could not confirm the order of the other three with a handbook source.
Atactic polypropylene (P) has its methyl groups placed at random, cannot pack into a lattice and is amorphous, so it is last. This rules out options A, B and C, which each place P above at least one crystallisable polymer. Syndiotactic polystyrene (Q) is regular and does crystallise, but the bulky phenyl rings make it crystallise slowly. Nylon 6 (R) and PET (S) are the classic semicrystalline polymers.
The order of PET and Nylon 6 in particular depends on the thermal and mechanical history of the sample and on how crystallinity is measured, and the order of the middle three can differ between sources. The key’s ranking is the usual textbook one; the explanation records it as the official answer and not as something I verified in a reference table.
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